help for rf transmnitter

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srimannarayanakarthik

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help for rf transmitter

i want to transmit data coming from serial port to another place.i mean i wanna receibe it at other end and want to control a device from it.i am definite to use a RF transmitter as i can increase my range of coverage.any suggestions?
what about rfPIC12c509AF......is it ok.
any more suggestions
 
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Probably OK, but it's complicated to use - and the receiver is even more complicated - it's MUCH easier to use licence free radio modules. Don't forget you need to include suitable coding routines - you can't use normal serial, see my tutorials for details.
 
I have done a similar project however not using a PIC but I suppose that's not a problem. I used an external RF transmitter and receiver, you can take a look at it **broken link removed** however if you want to build one transmitter/receiver on your own you can find some documentation on http://www.rfzone.org/free-rf-ebooks/. I hope this will help you a bit in your project. Good luck!!
 

its really useful for me.ill use the schematic. but i have a couple of doubts.
in the circuit what is the value of R1,what is IC2 and Q1.u didnt specify the values of them
ill use this circuit but with a different IC may be ATtiny2313,and ill use avr studio to program it instead of assembly as i am not aquited with it
 

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The above one is not my circuit.i just copied refa's circuit and attached it for reference.can i use any micro or is there any restriction on what micro i am using
 
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You can use any micro you like, it's just a question of writing the code for it. I notice the AVR circuit uses the TXD (internal UART) pin, this generally isn't a good idea, you can't reliably send normal serial data via a radio link. Again, try reading my tutorial at , which explains why.

As for the circuit above, it's just a standard micro-controller basic circuit, IC2 is obviously a 5V regulator (7805 or similar), Q1 is a 4MHz crystal (and is labelled as such), and the resistor is just a pullup resistor for the reset pin, and won't be at all critital - 10K should be fine?.
 
SIR,
Nigel Goodwin
I am using the ready rf module for serial data trans.
both end is working nicely [ tested on pc terminal ] but at the recevier side rxd_rf_moudle
send the data [ 00h ] continiously , which [ will ] make me difficault for work in other routine than the serial.
any simple solution to this simple prob. except any software logic.
thanks for your reply
 
If you read my tutorial it explains why, to do it properly you need to use Manchester coding (or some other NRZ system), although a 'bodge' which might get it working to some extent, is to add hardware inverters at each end.
 
i read your tutorial in that part,what you tell might be right,i understood the way to invert the signal and send it but wa not able to understand manchester coding.i just need send 0001,0010,0100,1000 throgh serial port and receive it a distance of 4 meters and contol a stepper motor using a FPGA,nios II processor.i can do the fpga part if i am able to receive the signal correctly.

now tell me for this distance and the above mentioned data transfer does the inveting mothod work?

i think we can invert the input by avrstudio.

there is no need for me to transmit a continous stram of data just a 4 bit data
 
The inverting method works, and 4m is no range at all - it's very easy to do, and shouldn't be a problem - I would suggest, as you only need four bits, that you use the other 4 bits of the 8 bit word to apply a little error checking, something as simple as duplicating the first four bits, but inverted, would provide some degree of error checking with little effort.
 
Nigel Goodwin said:
that you use the other 4 bits of the 8 bit word to apply a little error checking, something as simple as duplicating the first four bits, but inverted, would provide some degree of error checking with little effort.
Click to expand...

u mean to say that i should invert and send a signal xxxx1000 inorder to send 0001.how wil this correct my error i want to know how it is going to correct the RF signal
 
srimannarayanakarthik said:
u mean to say that i should invert and send a signal xxxx1000 inorder to send 0001.how wil this correct my error i want to know how it is going to correct the RF signal
Click to expand...

It won't correct it, but you can check to see if it's corrupted, and reject the data if it is.

For a start you need a hardware inverter at either end, IF you're using a hardware UART (for a software USART you can do it in software) - this gives the data more of a chance, because RS232 requires DC coupling, and a radio link is AC coupled.

To send '0001' as you're sending it as 8 bits, send it as '00011110' the second four bits being the inverted version of the first four. At the receiver side seperate the last four bits, invert them, and compare to the first four, if they aren't the same then reject the data as it's corrupted. This is a long way from foolproof, but it does give you a little extra checking, which for a link which isn't great to start with is well worth having, and takes hardly any effort to do.
 
Thanks for that help.ill try it now.can you tell me what exactly does uart and usart.i know that it means universal synchronous asynchronous receiver/transmitter
 
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UART is the one you need, a USART requires two connections, seperate clock and data lines - a UART just has data, the clock is specified to be the same at either end, and the start and stop bits syncronise it.
 
i want to learn completly of what i am doing.when i asked you the value of r1,how did you decide that is pull up resistpr and said as 10kohms.whats the criteria to decide the value of a compnenet imean resistor or capacitor.is it just the input voltage given or anything else?
 

It's just a pull-up resistor, it just needs to be low enough to pull the reset pin to a logic high, as the chip is CMOS this requires VERY little current, so it can be anywhere in a huge range.

From that you apply a little thought:

1) If it's too low then it will draw excessive current during reset, when you press the reset button the resistor is placed directly across the supply.

2) If it's too high the reset pin might be susceptible to external interference.

So choose a resistor that's not too low, and not too high - 10K seems a reasonable value, but so would 4.7K, or 22K - it really doesn't matter much.
 
Nigel Goodwin said:
For a start you need a hardware inverter at either end, IF you're using a hardware UART (for a software USART you can do it in software) - this gives the data more of a chance, because RS232 requires DC coupling, and a radio link is AC coupled.
Click to expand...
can you briefly explain briefly about how to invert the signal coming from the serial port.i am struck up with that part
 
srimannarayanakarthik said:
can you briefly explain briefly about how to invert the signal coming from the serial port.i am struck up with that part
Click to expand...

Any kind of inverter you wish?, here's a simple transistor example.
 

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